Pneumatic tires are sometimes constructed with a circumferential belt reinforcement positioned in their crown portion between tread and carcass. Such construction is often used with radial ply carcass tires and sometimes with bias ply tires.
The belt is typically a fabric-reinforced rubber in the form of a rubber encapsulated textile fabric, or multiple filament, such as steel, glass, nylon, aramid or polyester.
The belt reinforcement is used, for example, to control or limit the outward expansion or deformation of the tire in service, to provide some stability for the overall tire construction and to aid in providing a strengthening interface between the carcass plies and tread rubber.
Another and important purpose is to limit the distortion, or squirming, of the tread element as the tire rotates across a substrate (the ground or pavement, for example) and the tread passes through its footprint against the substrate. At this point of contact a considerable and continuing flexing and distortion of the tire is observed in the region of the footprint. Belt reinforcement resists such distortion at the footprint which usually results in better tread wear characteristics. However, internal heat generation and temperature build-up within the tire and belt reinforcement as the tread distorts and moves through the footprint stresses the integrity of the belt reinforcement and may adversely affect its durability, particularly at the belt edges in the region of the tire sidewalls.
It is well recognized that the shoulder region of the tire undergoes a large amount of flexing and distortion when the tire is used in service, particularly under load. As a result, it is the shoulder region of the tire in which a substantial amount of heat build-up occurs, resulting in an increased tire running temperature in this region. Therefore heat durability of a tire reinforcing belt positioned between its tread and carcass, particularly at the belt edges in the shoulder region of the joining of tread and sidewall, is an important concern.